CN112310358B - Negative electrode active material and secondary battery - Google Patents

Negative electrode active material and secondary battery Download PDF

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CN112310358B
CN112310358B CN201910688516.2A CN201910688516A CN112310358B CN 112310358 B CN112310358 B CN 112310358B CN 201910688516 A CN201910688516 A CN 201910688516A CN 112310358 B CN112310358 B CN 112310358B
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active material
negative electrode
electrode active
peak
material according
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CN112310358A (en
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梁成都
赵玉珍
官英杰
温严
黄起森
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to CN201910688516.2A priority Critical patent/CN112310358B/en
Priority to EP20847834.7A priority patent/EP3940824B1/en
Priority to PCT/CN2020/103346 priority patent/WO2021017956A1/en
Priority to KR1020217030666A priority patent/KR102468592B1/en
Priority to JP2021554377A priority patent/JP7261898B2/en
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Abstract

The invention belongs to the technical field of energy storage, and particularly discloses a negative active material which comprises SiOxParticles and coated SiOxA modified polymer coating of the particles, wherein 0<x<2; the Raman shift of the negative active material is 280cm‑1～345cm‑1Intensity of peak in the range of I1The Raman shift of the negative active material is 450cm‑1～530cm‑1Intensity of peak in the range of I2The Raman shift of the cathode active material is 900cm‑1～960cm‑1Intensity of peak in the range of I3And 0.1. ltoreq.I1/I2≤0.6，0.2≤I3/I2Less than or equal to 1.0. The invention also discloses a method for preparing the negative active material and a secondary battery. The negative active material can improve the cycle performance of the secondary battery and improve the energy density of the secondary battery.

Description

Negative electrode active material and secondary battery
Technical Field
The invention belongs to the technical field of energy storage, and particularly relates to a negative electrode active material and a secondary battery.
Background
With the increasing emphasis on environmental protection, environmentally friendly power type secondary batteries are increasingly being applied to electric vehicles. Unlike secondary batteries for consumer electronics, power-type secondary batteries have higher requirements for energy density and cycle life. Silicon oxide has a high theoretical gram capacity as a negative electrode active material, which is several times that of a graphite-based negative electrode active material, compared to a conventional carbon material, and thus, it is expected to improve the energy density of a secondary battery using silicon oxide.
However, the silicon oxide has a poor cycle life, which causes deterioration of cycle performance of the secondary battery. Therefore, it is urgently required to develop a new anode active material for a secondary battery having both long cycle performance and high energy density.
Disclosure of Invention
In view of the problems of the background art, the present invention provides a negative electrode active material, and a secondary battery using the negative electrode active material has both longer cycle performance and higher energy density.
To achieve the above object, a first aspect of the present invention provides a negative active material comprising SiOxParticles and coated SiOxA modified polymer coating of the particles, wherein 0<x<2; the Raman shift of the negative active material is 280cm-1～345cm-1Intensity of the (scattered) peak in the range I1The Raman shift of the negative active material is 450cm-1～530cm-1Intensity of the (scattered) peak in the range I2The Raman shift of the cathode active material is 900cm-1～960cm-1Intensity of the (scattered) peak in the range I3And 0.1. ltoreq.I1/I2≤0.6，0.2≤I3/I2≤1.0。
Without being bound by theory, the anode active material of the present invention has a Raman shift of 450cm-1～530cm-1The scattering peaks in the range are ascribed to the silicon oxide compound (hereinafter abbreviated as SiO)xPeaks); the anode active material of the invention has a Raman shift of 280cm-1～345cm-1The scattering peak in the range is attributed to a C-S bond (hereinafter, simply referred to as a C-S peak) which causes the coating layer to have higher toughness; the Raman shift of the cathode active material is 900cm-1～960cm-1The scattering peak in the range is attributed to S-S bonds (hereinafter referred to as S-S peaks) which enable the coating layer to have high active ion conductivity, and the S-S bonds are broken and combined with active ions during charging of the battery to perform ion migration and have high migrationThe speed, active ions are removed in the discharging process of the battery, S-S bonds are recombined, the breakage and the bonding of the S-S bonds are only generated in the charging and discharging process of the battery, the structure of the carbon-based framework is kept unchanged, and the protective effect of the coating layer on the silica compound is ensured.
Without being bound by theory, the SiO in the negative active material of the present inventionxHas higher gram capacity and longer cycle life, and improves the cycle performance and energy density of the secondary battery.
Without being limited by theory, the modified polymer coating layer in the cathode active material has strong toughness and can be well adapted to SiOxExpansion and contraction of material in lithium extraction process, on SiOxThe material has a protection effect, has high active ion conduction performance, inhibits the side reaction of electrolyte on the surface of the material, and ensures that SiOxThe gram capacity of the material is exerted, the consumption of active lithium ions is reduced, and the irreversible capacity of the battery is reduced, so that the coulombic efficiency and the cycle performance of the secondary battery are improved.
In some embodiments of the first aspect of the present invention, I is 0.15 ≦ I1/I2Less than or equal to 0.4. Peak intensity of C-S peak and SiOxThe peak intensity of the peak meets the relationship, so that the coating layer has better toughness, can adapt to the expansion and contraction of the silicon-oxygen compound in the process of releasing and inserting lithium, has a protection effect on the silicon-oxygen compound, and inhibits the side reaction of the electrolyte on the surface of the material, thereby further improving the charge-discharge cycle life of the battery.
In some embodiments of the first aspect of the present invention, I is 0.3 ≦ I3/I2Less than or equal to 0.8. Peak intensity of S-S peak and SiOxThe peak intensity of the peak meets the relationship, so that the coating layer has better active ion conduction performance, and the rate capability and the charge-discharge cycle life of the material are further improved.
In some embodiments of the first aspect of the present invention, the coating is a partial coating and/or a full coating; preferably, the coating is a full coating.
In some embodiments of the first aspect of the present invention, the coating is a contact coating and/or a non-contact coating, whichIn the contact coating, the modified polymer coating layer is coated with SiOxParticles and SiOxThe surface of the particles is contacted, whereas the non-contact coating means that the modified polymer coating coats SiOxParticles but with SiOxThe particle surfaces do not touch.
In some embodiments of the first aspect of the present invention, 0.5 ≦ x ≦ 1.6, preferably x is close to 1, 0.9 ≦ x ≦ 1.2, e.g., 1. SiO 2xThe value of x is in the range, which is beneficial to ensuring that the cathode active material has higher gram capacity and longer cycle life, thereby improving the cycle performance and energy density of the secondary battery.
In some embodiments of the first aspect of the present disclosure, the anode active material has a raman shift of 1300cm-1～1380cm-1Intensity of the (scattered) peak in the range IDThe Raman shift of the negative active material is 1520cm-1～1590cm-1Intensity of the (scattered) peak in the range IGAnd, 1.05. ltoreq.ID/IG≤1.50。
In some embodiments of the first aspect of the present invention, 1.1 ≦ ID/IGLess than or equal to 1.45. Peak intensity of D peak IDPeak intensity of G peak IGThe ratio of the positive electrode active material to the negative electrode active material is within the range, so that the irreversible capacity of the material in charge-discharge cycles can be reduced, the coating layer is ensured to have better conductivity, the capacity of the material can be fully exerted, the cycle capacity retention rate of the material is further improved, and the cycle performance and the energy density of a secondary battery adopting the negative electrode active materials are further improved.
In some embodiments of the first aspect of the present invention, ID/IGThe upper limit of (d) may be any one of 1.5, 1.48, 1.45, 1.42, 1.40, 1.37, 1.35, 1.33, 1.30; i isD/IGThe lower limit of (b) may be any one of values of 1.28, 1.25, 1.23, 1.20, 1.18, 1.15, 1.12, 1.10, 1.08, 1.05; i.e. ID/IGThe range of (b) may be formed by a combination of any of the upper and lower numerical values set forth above.
In some embodiments of the first aspect of the present invention, the negative active materialAt a Raman shift of 1300cm-1～1380cm-1The half-peak width of the (scattered) peak in the range was 120cm-1～160cm-1Preferably 128cm-1～152cm-1。
In the raman spectrum of the negative electrode active material, the half-value width of the D peak is preferably 120cm or more-1More preferably equal to or greater than 128cm-1The elasticity and toughness of the coating layer can be further improved, so that the coating layer can better adapt to the expansion and contraction of the silicon-oxygen compound in the charging and discharging processes without cracking. The half-value width of the D peak is preferably 160cm or less-1More preferably 152cm or less-1The coating layer can be ensured to have higher conductivity, and the cycle performance of the secondary battery is further improved.
In some embodiments of the first aspect of the present invention, the aforementioned scattering peaks in the raman shift range comprise scattering peaks at the end points of the raman shift.
In some embodiments of the first aspect of the present invention, the modified polymer coating comprises elemental sulfur and elemental carbon.
In some embodiments of the first aspect of the present invention, the elemental sulfur is present in an amount of 0.5% to 3%, preferably 0.8% to 1.5%, by mass of the anode active material.
The content of sulfur element in the negative active material is preferably more than 0.5%, preferably more than 0.8%, the content of C-S and-S-S-groups in the coating layer can be further increased, the toughness of the coating layer and the conduction rate of active ions are further improved, and the polarization of the battery is reduced. The content of the sulfur element is less than 3 percent, preferably less than 1.5 percent, on one hand, the coating layer has higher toughness and ion conduction rate and also has lower thickness so as to further reduce the reduction degree of material capacity caused by the increase of the content of the coating layer; on the other hand, the elemental sulfur residue in the material is further reduced, so that the capacity loss degree of the material caused by the completely irreversible reaction of the elemental sulfur and the active ions is further reduced. Therefore, the content of elemental sulfur in the negative electrode active material is within the above range, and the cycle performance and energy density of the secondary battery can be further improved.
In some embodiments of the first aspect of the present invention, the carbon element accounts for 0.1 to 4% by mass, preferably 0.5 to 3% by mass of the anode active material. The content of carbon element in the negative active material is in the range, so that the coating layer has higher electron conductivity, the coating layer has better elasticity and toughness, and the silicon-oxygen compound is better protected, thereby further improving the cycle performance and energy density of the secondary battery.
In some embodiments of the first aspect of the present invention, the modified polymer coating is formed by heat treating a polymer with sulfur powder in an inert atmosphere; preferably, the polymer is selected from at least one of polyacrylonitrile, polyaniline, polyethylene, polyacetylene, polyvinyl chloride and polystyrene;
preferably, the temperature of the heat treatment is 250 ℃ to 450 ℃, more preferably 300 ℃ to 450 ℃;
preferably, the mass ratio of the sulfur powder to the polymer is (1-5): 1, more preferably (2-4): 1;
preferably, the heat treatment time is 2-8 hours, more preferably 3-5 hours;
preferably, the inert atmosphere is selected from one or more of a nitrogen atmosphere, an argon atmosphere and a helium atmosphere.
In some embodiments of the first aspect of the present invention, the negative active material has a peak with a half-value width of 4 ° to 12 °, preferably 5 ° to 10 °, in a range of 19 ° to 27 ° in 2 θ in an X-ray diffraction spectrum. The negative active material having a diffraction peak at a position where 2 theta is 19 DEG to 27 DEG and a half-value width within a given range has a higher gram capacity and a lower cycle expansion, and is less likely to be cracked and pulverized during charge and discharge cycles of a secondary battery, so that the cycle life of the battery can be further improved.
In some embodiments of the first aspect of the present disclosure, the particle size D of the negative electrode active material v50 is 2 to 12 μm, preferably 4 to 8 μm.
The average particle size Dv50 of the negative electrode active material is preferably 2 μm or more, more preferably 4 μm or more, and can reduce film formation consumption of active ions in the negative electrode and side reactions of the electrolyte in the negative electrode, thereby reducing the irreversible capacity of the secondary battery and improving the cycle performance of the secondary battery; the amount of binder added in the negative electrode can also be reduced, which is advantageous in improving the energy density of the secondary battery.
The average particle diameter Dv50 of the negative electrode active material is preferably 12 μm or less, more preferably 8 μm or less, which is advantageous for improving the conduction rate of active ions and electrons, and also for preventing the particles from being cracked or pulverized during charge and discharge, thereby improving the cycle performance of the secondary battery.
In some embodiments of the first aspect of the present disclosure, the particle size D of the negative electrode active materialv10. Particle diameter D v50 and particle diameter Dv90 satisfies the following conditions: not more than 0.5 (D)v90-Dv10)/D v50 is less than or equal to 2.5. The negative active material with the particle size distribution can reduce the side reaction of a negative diaphragm, reduce the consumption of electrolyte, and is beneficial to preventing particles from cracking or breaking in the charging and discharging process, so that the structural stability of the material is improved, and the cycle performance of the battery is further improved.
In some embodiments of the first aspect of the invention, 0.8 ≦ (D)v90-Dv10)/D v50≤2.0。
In some embodiments of the first aspect of the present disclosure, the negative active material has a specific surface area of 0.5m2/g～5m2A/g, preferably of 0.8m2/g～3m2G, e.g. 1m2/g、1.2m2/g、1.5m2/g、1.7m2/g、1.9m2/g、2m2/g、2.1m2/g、2.3m2/g、2.5m2/g、2.7m2/g、3m2/g、3.1m2/g、3.3m2/g、3.5m2/g、3.7m2/g、3.9m2/g、4m2/g、4.2m2/g、4.4m2/g、4.6m2/g、4.8m2/g、4.9m2/g。
The specific surface area of the negative electrode active material is preferably 0.5m2More than g, preferably 0.8m2More than g, the surface of the material has more active sites, the electrochemical performance of the material can be improved, and the requirements of secondary batteries on the dynamic performance and the times are metRate performance requirements. The specific surface area of the negative electrode active material is preferably 5m2A ratio of less than g, preferably 3m2The concentration of the active ion is less than or equal to/g, so that the side reaction of the electrolyte on the negative electrode is reduced, the film forming consumption of the active ion on the negative electrode can be reduced, and the cycle performance of the battery is improved.
In some embodiments of the first aspect of the present disclosure, the negative active material has a tap density of 0.8g/cm3～1.3g/cm3Preferably 0.9g/cm3～1.2g/cm3. The tap density of the negative electrode active material is within a given range, which is advantageous for improving the energy density of the secondary battery.
In some embodiments of the first aspect of the present disclosure, the negative active material is depressurized after 30 seconds of pressure holding at 5 tons, and the measured compacted density is 1.1g/cm3～1.6g/cm3Preferably 1.2g/cm3～1.5g/cm3. The compaction density of the negative electrode active material measured by pressure relief after pressure maintaining for 30s under the pressure of 5 tons is in a given range, which is beneficial to improving the energy density of the secondary battery.
The raman spectrum of the negative active material can be measured by instruments and methods known in the art, for example, by a raman spectrometer, for example, a LabRAM HR Evolution type laser micro-raman spectrometer can also be used.
In the present invention, the (scattering) peak intensity of the negative electrode active material in a certain raman shift range refers to the maximum value of the intensity values in the raman shift range in the raman spectrum.
The X-ray diffraction spectrum of the negative active material can be measured by an apparatus and a method known in the art. The X-ray diffraction spectrum is measured, for example, by an X-ray diffractometer according to JIS K0131-1996X-ray diffraction analysis general rules.
The contents of the sulfur element and the carbon element in the negative active material can be measured by an apparatus and a method known in the art. For example, the test is carried out according to GB/T20123-2006/ISO 15350:2000JJG 395-1997 by using an HCS-140 carbon content analyzer.
Particle diameter D of negative electrode active materialv10、D v50 and Dv90 are all as known in the art and can be usedThe measurement is carried out using instruments and methods known in the art. This may conveniently be done, for example, using a laser particle size analyser, such as the Mastersizer3000 laser particle size analyser from malvern instruments ltd, uk.
The specific surface area of the negative electrode active material is known in the art and can be determined by an apparatus and a method known in the art, for example, by referring to GB/T19587-.
The tap density of the negative active material is a term well known in the art and can be conveniently determined using an apparatus and method well known in the art, such as a tap density meter, for example, a BT-300 type tap density meter.
The compacted density of the negative active material is a term well known in the art and can be determined using instruments and methods well known in the art. For example, the measurement can be carried out by an electronic pressure tester (e.g., UTM7305 type electronic pressure tester) according to GB/T243358-2009. Weighing 1g of negative electrode active material, adding into the negative electrode active material with a bottom area of 1.327cm2The pressure was maintained for 30s, then the pressure was released, 10s was maintained, and then the compacted density of the negative electrode active material was recorded and calculated.
The second aspect of the present invention relates to a method for producing an anode active material, comprising the following steps (1), (2), (3), optional step (2-1), and optional step (3-1):
(1) dissolving a certain mass of polymer in a solvent to obtain a solution; wherein the polymer is selected from at least one of polyacrylonitrile, polyaniline, polyethylene, polyacetylene, polyvinyl chloride and polystyrene;
(2-1) SiOxThe material is crushed to obtain SiO with certain particle sizexParticles, wherein x is more than 0 and less than 2;
(2) mixing SiOxThe particles and the solution obtained in step (1)Mixing the two phases to obtain a mixture, wherein x is more than 0 and less than 2;
(3-1) drying the mixture obtained in the step (2) to obtain a solid;
(3) and (3) mixing the mixture obtained in the step (2) or the solid obtained in the step (3-1) with a certain mass of sulfur powder, and then carrying out heat treatment in an inert atmosphere to obtain the negative electrode active material.
In some embodiments of the second aspect of the present invention, SiOxThe particles are SiO with certain particle size sold in the marketxAnd (3) granules.
In some embodiments of the second aspect of the present invention, in step (1), the solvent is at least one selected from the group consisting of dimethylformamide, N-methylpyrrolidone, xylene, and toluene.
In some embodiments of the second aspect of the present invention, in step (1), the polymer to solvent ratio is from 0.1g/L to 10g/L, preferably from 1g/L to 5g/L, for example 0.7g/L, 2g/L, 3g/L, 4g/L, 5g/L, 6g/L, 7g/L, 8g/L, 9 g/L.
In certain embodiments of the second aspect of the present invention, the SiO in step (2)xThe mass ratio of the particles to the polymer in step (1) is 10-200, preferably 20-100, such as 15, 25, 30, 35, 45, 40, 50, 55, 60, 65, 70, 75, 80, 85, 90, 110, 120, 130, 150, 170, 190. The higher the mass content of the polymer, the higher the content of carbon element in the coating layer of the negative electrode active material. The mass ratio of the silicon-oxygen compound to the polymer is in the range, the protective effect of the coating layer on the silicon-oxygen compound is ensured, the negative active material can be effectively prevented from agglomerating in the preparation process, and the material is favorable for having higher active ion conduction performance in the charging and discharging processes.
In some embodiments of the second aspect of the present invention, in step (3-1), the drying temperature is 80 ℃ to 250 ℃, preferably 110 ℃ to 200 ℃, for example 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃, 200 ℃, 230 ℃, 250 ℃.
In some embodiments of the second aspect of the present invention, in step (3-1), the drying time is 0.5 to 10 hours, preferably 1 to 9 hours, such as 2, 3, 4, 5, 6, 7, 8, 9 hours.
In some embodiments of the second aspect of the present invention, in step (3-1), the temperature increase rate during drying is 1 to 10 ℃/min, preferably 1 to 5 ℃/min.
In some embodiments of the second aspect of the present invention, in step (3-1), the drying is performed in an inert atmosphere;
preferably, the inert atmosphere is selected from one or more of a nitrogen atmosphere, an argon atmosphere and a helium atmosphere.
In some embodiments of the second aspect of the present invention, in step (3-1), the mixture may be dried using equipment and methods known in the art, such as vacuum drying, pneumatic drying, spray drying, and the like. As an example, a wet-process cladding machine may be used.
Without being limited by theory, in the step (3), the sulfur powder and the polymer are subjected to a crosslinking reaction in an inert atmosphere, so that the elasticity and toughness of the coating layer are improved, and the ion conductivity of the coating layer is improved, thereby improving the cycle performance of the battery.
In some embodiments of the second aspect of the present invention, in step (3), the temperature of the heat treatment is 250 ℃ to 450 ℃, preferably 300 ℃ to 450 ℃, such as 250 ℃, 270 ℃, 280 ℃, 300 ℃, 320 ℃, 350 ℃, 360 ℃, 380 ℃, 400 ℃, 420 ℃, 440 ℃, 450 ℃; the heat treatment temperature is in the range, so that the coating layer can not be completely carbonized, the elasticity and toughness of the coating layer can be further improved, and the expansion and contraction of the silicon-oxygen compound in the charging and discharging processes can be better adapted; and the obtained coating layer can effectively isolate the silicon-oxygen compound from the electrolyte, reduce side reactions and improve the cycle performance of the battery.
In some embodiments of the second aspect of the present invention, in the step (3), the heat treatment time is 2 to 8 hours, preferably 3 to 5 hours.
In some embodiments of the second aspect of the present invention, in the step (3), the inert atmosphere is selected from one or more of a nitrogen atmosphere, an argon atmosphere and a helium atmosphere.
In some embodiments of the second aspect of the present invention, the mass ratio of sulfur powder to polymer is (1-5): 1, preferably (2-4): 1; the mass ratio of the sulfur powder to the polymer is in the range, so that the coating layer of the cathode active material has high electron conductivity and active ion conductivity, elemental sulfur residue in the coating layer is avoided, capacity loss caused by irreversible reaction between residual elemental sulfur and active ions is effectively prevented, and the battery has high cycle performance. In addition, the mass ratio of the sulfur powder to the polymer is within the above range, so that the sulfur powder can fully crosslink the polymer, and the elasticity and toughness of the coating layer can be improved.
The negative electrode active material prepared by the method of the second aspect of the present invention is the negative electrode active material of the first aspect of the present invention.
In some embodiments of the present invention, the polyacrylonitrile, polyaniline, polyethylene, polyacetylene, polyvinyl chloride, or polystyrene has a weight average molecular weight of 5 to 20 ten thousand, preferably 5 to 15 ten thousand.
In some embodiments of the present invention, the molecular weight distribution coefficient of polyacrylonitrile, polyaniline, polyethylene, polyacetylene, polyvinyl chloride or polystyrene is a molecular weight distribution coefficient known in the art, for example, 1.1 to 1.5, preferably 1.2 to 1.5.
In some embodiments of the invention, SiOxThe particle size of the particles is 1.5 to 11 μm, preferably 2 to 7.5. mu.m.
A third aspect of the invention provides a secondary battery comprising the anode active material of the first aspect of the invention.
The secondary battery of the present invention has both long cycle performance and high energy density.
In some embodiments of the third aspect of the present invention, the secondary battery comprises a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises the negative electrode active material of the first aspect of the present invention.
In some embodiments of the third aspect of the present invention, the negative electrode current collector is made of a material having good conductivity and mechanical strength, such as copper foil.
In some embodiments of the third aspect of the present invention, the negative electrode film layer further includes a carbon material, and the carbon material is selected from one or more of artificial graphite, natural graphite, mesophase micro carbon spheres (MCMB), hard carbon, and soft carbon, and preferably, the carbon material is selected from one or more of artificial graphite and natural graphite.
In some embodiments of the third aspect of the present invention, the negative electrode film layer further includes one or more selected from a conductive agent, a binder and a thickener, and the kind of the one or more selected from the group consisting of the conductive agent, the binder and the thickener is not particularly limited, and can be selected by a person skilled in the art according to actual needs.
The conductive agent includes, but is not limited to, graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
The binder includes, but is not limited to, polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyvinyl alcohol (PVA), Styrene Butadiene Rubber (SBR), sodium carboxymethyl cellulose (CMC), Sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCs).
The thickener includes, but is not limited to, sodium carboxymethylcellulose (CMC).
The negative electrode sheet may be prepared according to methods conventional in the art, such as a coating method. As an example, a negative electrode active material, and optionally a conductive agent, a binder, and a thickener are dispersed in a solvent, which may be deionized water, to form a uniform negative electrode slurry, and the negative electrode slurry is coated on a negative electrode current collector, and subjected to drying, cold pressing, and the like, to obtain a negative electrode sheet.
In some embodiments of the third aspect of the present invention, the positive electrode sheet includes a positive electrode collector and a positive electrode film layer disposed on at least one surface of the positive electrode collector and including a positive electrode active material. The kind of the positive electrode active material in the present invention is not particularly limited, and those skilled in the art can select a positive electrode active material that can be used for a secondary battery according to actual needs.
The positive active material includes, but is not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and olivine-structured lithium-containing phosphate.
In some embodiments of the third aspect of the present invention, the positive electrode current collector is made of a material having good electrical conductivity and mechanical strength, and is preferably an aluminum foil.
In some embodiments of the third aspect of the present invention, the positive electrode film layer further includes a binder and/or a conductive agent, and the kind of the binder and the conductive agent is not particularly limited, and can be selected by a person skilled in the art according to actual needs.
Binders include, but are not limited to, polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE).
Conductive agents include, but are not limited to, graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
The positive electrode sheet can be prepared according to a conventional method in the field, such as a coating method. As an example, a positive electrode active material, and optionally a conductive agent and a binder are dispersed in a solvent, where the solvent may be N-methylpyrrolidone, to form a uniform positive electrode slurry, and the positive electrode slurry is coated on a positive electrode current collector, and subjected to drying, cold pressing, and the like, to obtain a positive electrode sheet.
In some embodiments of the third aspect of the present invention, the electrolyte may be a solid or gel electrolyte, or may be a liquid electrolyte (i.e., an electrolyte solution), and an electrolyte salt containing active ions may be dispersed in an organic solvent to form the electrolyte solution.
Electrolyte salts include, but are not limited to, LiPF6(lithium hexafluorophosphate), LiBF4Lithium tetrafluoroborate (LiClO), LiClO4(lithium perchlorate) LiAsF6(lithium hexafluoroarsenate), LiFSI (lithium bis (fluorosulfonylimide), LiTFSI (lithium bis (trifluoromethanesulfonylimide)), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalato borate), LiBOB (lithium dioxaoxalato borate), LiPO2F2(lithium difluorophosphate), LiDFOP (lithium difluorooxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate).
Solvents include, but are not limited to, Ethylene Carbonate (EC), Propylene Carbonate (PC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Butylene Carbonate (BC), fluoroethylene carbonate (FEC), Methyl Formate (MF), Methyl Acetate (MA), Ethyl Acetate (EA), Propyl Acetate (PA), Methyl Propionate (MP), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB), Ethyl Butyrate (EB), 1, 4-butyrolactone (GBL), Sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).
In some embodiments of the third aspect of the present invention, the electrolyte further comprises an additive, wherein the kind of the additive is not particularly limited and may be selected according to the requirement. For example, the additive can comprise a negative electrode film forming additive, can also comprise a positive electrode film forming additive, and can also comprise an additive capable of improving certain performances of the battery, such as an additive capable of improving the overcharge performance of the battery, an additive capable of improving the high-temperature performance of the battery, an additive capable of improving the low-temperature performance of the battery, and the like.
In some embodiments of the third aspect of the present invention, the separator is disposed between the positive electrode plate and the negative electrode plate to perform a separation function. The kind of the separator is not particularly limited, and any known separator having a porous structure with good chemical stability and mechanical stability, such as one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, may be used. The separating film can be a single-layer film or a multi-layer composite film. When the barrier film is a multilayer composite film, the materials of the layers may be the same or different.
The secondary battery can be prepared according to conventional methods in the art, for example, a positive electrode plate, a separator, and a negative electrode plate are sequentially wound (or laminated), the separator is positioned between the positive electrode plate and the negative electrode plate to perform the separation function, so as to obtain an electrical core, the electrical core is placed in an outer package, and an electrolyte is injected and sealed, so as to obtain the secondary battery.
For the sake of brevity, only some numerical ranges are explicitly disclosed herein. However, ranges formed by any lower limit in combination with any upper limit, ranges formed by any lower limit in combination with other lower limits, and ranges formed by any upper limit in combination with any other upper limit are within the scope of the invention. Further, every point or individual numerical value between the upper and lower limits of any range is included in the claimed range, and every point or individual numerical value may be included in the range formed by combining the lower limit or upper limit with any other point or individual numerical value or with other lower limit or upper limit as the range formed by combining the lower limit or upper limit with other lower limit or upper limit, within the scope of the present invention.
In the description herein, it is to be noted that, unless otherwise specified, "above" and "below" are inclusive, and "one or more" means "several" are two or more.
Compared with the prior art, the invention has at least the following beneficial effects:
the negative active material of the present invention comprises SiOx(0<x<2) And coating on SiOx(0<x<2) At least one part of the outer surface of the modified polymer coating layer is coated on the anode active material, and the Raman shift of the anode active material is 280cm-1～345cm-1Intensity of peak in the range of I1The Raman shift of the negative active material is 450cm-1～530cm-1Intensity of peak in the range of I2The Raman shift of the cathode active material is 900cm-1～960cm-1Intensity of peak in the range of I3And 0.1. ltoreq.I1/I2≤0.6，0.2≤I3/I2Less than or equal to 1.0; the modified polymer coating layer has high toughness and high ion conductivity, and the circulating coulombic efficiency of the material is improved, so that the circulating performance of the secondary battery is greatly improved.
The cycle performance of a secondary battery using the negative electrode active material of the present invention is improved, and the energy density is improved.
Drawings
Fig. 1 is a raman spectrum of a negative active material in an embodiment of the present invention;
fig. 2 is an X-ray diffraction spectrum of one negative active material in the example of the present invention.
Detailed Description
The present disclosure is more particularly described in the following examples that are intended as illustrations only, since various modifications and changes within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the equipment used in the examples is commercially available.
Example 1
(1) Preparation of negative active material:
adding 0.7g of polyacrylonitrile (the weight-average molecular weight is 5-15 ten thousand, and the molecular weight distribution coefficient is 1.2-1.5) into 1L of dimethylformamide, and stirring until the polyacrylonitrile is completely dissolved to obtain a solution;
adding 100g of silicon monoxide (SiO, the particle size is 1.5-11 mu m) into the solution and stirring to obtain mixed slurry;
thirdly, keeping the temperature of the mixed slurry at 180 ℃ for 2 hours in an argon atmosphere to obtain solid powder;
and fourthly, weighing 1.4g of sulfur powder (the purity is more than 99.9 percent) and mixing the sulfur powder with the solid powder, carrying out heat treatment for 3h at 380 ℃ in an argon atmosphere, and cooling to obtain the negative electrode active material.
(2) Preparing a button cell:
and mixing the prepared negative active material with artificial graphite according to a mass ratio of 3:7 to obtain a negative active material. Fully stirring and mixing a negative electrode active substance, conductive carbon black Super P serving as a conductive agent, Styrene Butadiene Rubber (SBR) serving as a binder and sodium carboxymethyl cellulose (CMC) in a proper amount of deionized water according to the weight ratio of 88:3:6:3 to form uniform negative electrode slurry; and coating the negative electrode slurry on a copper foil of a negative current collector, drying and cold-pressing to obtain an electrode plate, wherein the electrode plate can be used as a negative electrode plate in a secondary battery.
And (3) taking a metal lithium sheet as a counter electrode, adopting a Celgard 2400-type industrial polypropylene membrane as a separation membrane, injecting electrolyte, and assembling to obtain the button cell. Wherein the electrolyte is prepared by uniformly mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) according to the volume ratio of 1:1:1 to obtain an organic solvent, and then, LiPF6Dissolving in the organic solvent, adding fluoroethylene carbonate (FEC) as additive, and adding LiPF in electrolyte6The concentration of (2) is 1mol/L, and the mass ratio of FEC in the electrolyte is 6%.
Examples 2 to 13
The parameters of examples 2-13 in Table 1 are used to prepare the negative active material, the particle size of SiO used in example 10 is 2-3.5 μm, the particle size of SiO used in example 11 is 7-9 μm, the particle size of SiO used in example 12 is 2-2.5 μm, the particle size of SiO used in example 13 is 4-5 μm, the rest are the same as example 1, and the button cell is prepared the same as example 1.
Table 1: preparation parameters of negative active material
Figure BDA0002147124500000161
Comparative examples 1 to 4
The negative active material was prepared using the parameters of comparative examples 1-4 in table 1, the rest of which is the same as example 1, and the button cell was prepared as in example 1.
Testing of negative active materials
1) Raman spectroscopic analysis
The negative active materials in the examples and comparative examples were measured by using a LabRAM HR Evolution type laser micro-Raman spectrometer, in which a solid laser with a wavelength of 523nm was used as a light source, the beam diameter was 1.2 μm, and the power was 1 mW; the measurement mode adopts macroscopic Raman; a CCD detector is used. The negative active material powder was tabletted, 3 points were randomly selected on the tablet for testing, and the average value was taken. The raman spectrum of one of the negative active materials in the examples is shown in fig. 1.
Will shift at a Raman of 280cm-1～345cm-1The intensity of the scattered peak at the position is recorded as I1At a Raman shift of 450cm-1～530cm-1The intensity of the scattered peak at the position is recorded as I2At a Raman shift of 900cm-1～960cm-1The intensity of the scattered peak at the position is recorded as I3At a Raman shift of 1300cm-1～1380cm-1The intensity of the scattered peak at the position is recorded as IDAt Raman shift 1520cm-1～1590cm-1The intensity of the scattered peak at the position is recorded as IGThe results are shown in Table 2.
2) XRD spectral analysis
The negative active materials in the respective examples and comparative examples were measured by a Bruker D8Discover type X-ray diffractometer as CuKαThe radiation is radiation source, and the wavelength of the radiation
Figure BDA0002147124500000171
The angle range of the scanning 2 theta is 15-80 degrees, and the scanning speed is 4 degrees/min. Wherein, the XRD spectrum of one negative active material in the example is shown in figure 2.
3) Detection of specific surface area and particle diameter
The specific surface area of the negative active materials of each example and each comparative example are calculated by adopting a nitrogen adsorption specific surface area analysis test method and a BET (Brunauer Emmett Teller) method according to a standard of determining the specific surface area of a solid substance by a GB/T19587-2004 gas adsorption BET method; the nitrogen adsorption specific surface area analysis test can be carried out by a Tri Star II 3020 specific surface area and pore analyzer from Micromeritics, USA.
Detecting the particle diameters D of the anode active materials 1-12 and A-E by adopting a Mastersizer3000 type laser particle size analyzer of British Malvern instruments Ltdv10. Dv50, particle size Dv90, and the particle size distribution was calculated according to the following formula.
Particle size distribution ═ Dv90-Dv10)/D v50
The results are shown in Table 2.
4) First coulombic efficiency and cycle performance test
Under the environment of 25 ℃ and normal pressure, discharging the button cell with constant current at 0.1C multiplying power until the voltage is 0.005V, then discharging with constant current at 0.05C multiplying power until the voltage is 0.005V, and recording the discharge specific capacity at the moment, namely the first lithium intercalation capacity; and then, carrying out constant current charging at a multiplying power of 0.1C until the voltage is 1.5V, and recording the charging specific capacity at the moment, namely the first lithium removal capacity. The button cell was subjected to 50 cycles of charge and discharge tests according to the above method, and the lithium removal capacity was recorded for each time.
First coulombic efficiency (%) of the negative electrode active material was first delithiation capacity/first intercalation capacity × 100%
The cycle capacity retention ratio (%) of the negative electrode active material was 50 th delithiation capacity/first delithiation capacity × 100%
The results are shown in Table 2.
Table 2: test results
Figure BDA0002147124500000181
Figure BDA0002147124500000191
Note: "/" indicates that the material does not have this scattering peak.
As can be seen from Table 2:
the negative active material comprises a silicon-oxygen compound and a coating layer coated on the outer surface of the silicon-oxygen compound. The anode active material of the invention has a Raman shift of 280cm-1～345cm-1、450cm-1～530cm-1、900cm-1～960cm-1Has a scattering peak at a position of (1), wherein I is 0.1. ltoreq. I1/I2≤0.6，0.2≤I3/I2The ratio of the total amount of the active material to the total amount of the active material is less than or equal to 1.0, so that the negative active material has higher first coulombic efficiency and longer cycle life compared with the negative active materials of comparative examples 1-4; particularly satisfies 0.15. ltoreq.I1/I2I is not less than 0.4 and not more than 0.33/I2First coulombic efficiency and cycle of the negative active material of the invention less than or equal to 0.8The ring life is further improved. Therefore, the negative active material can improve the energy density, the first coulombic efficiency and the cycle performance of the secondary battery.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications and substitutions can be easily made by those skilled in the art within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (30)

1. An anode active material comprising SiOxParticles and coated SiOxA modified polymer coating of the particles, wherein 0<x<2; the modified polymer coating layer is formed by heat treatment of a polymer and sulfur powder in an inert atmosphere, wherein the polymer is selected from at least one of polyacrylonitrile, polyaniline, polyethylene, polyacetylene, polyvinyl chloride and polystyrene;
the Raman shift of the negative active material is 280cm-1～345cm-1Intensity of peak in the range of I1The Raman shift of the negative active material is 450cm-1～530cm-1Intensity of peak in the range of I2The Raman shift of the cathode active material is 900cm-1～960cm-1Intensity of peak in the range of I3And 0.1. ltoreq.I1/I2≤0.6，0.2≤I3/I2≤1.0。
2. The negative electrode active material according to claim 1, wherein I is 0.15. ltoreq.I1/I2≤0.4。
3. The negative electrode active material according to claim 1, wherein 0.3. ltoreq.I3/I2≤0.8。
4. The negative electrode active material according to any one of claims 1 to 3, characterized in thatThen, the Raman shift of the cathode active material is 1300cm-1～1380cm-1Intensity of peak in the range of IDThe Raman shift of the negative active material is 1520cm-1～1590cm-1Intensity of peak in the range of IGAnd, 1.05. ltoreq.ID/IG≤1.50。
5. The negative electrode active material according to any one of claims 1 to 3, wherein the negative electrode active material has a Raman shift of 1300cm-1～1380cm-1Intensity of peak in the range of IDThe Raman shift of the negative active material is 1520cm-1～1590cm-1Intensity of peak in the range of IGAnd, 1.1. ltoreq.ID/IG≤1.45。
6. The negative electrode active material according to any one of claims 1 to 3, wherein the negative electrode active material has a Raman shift of 1300cm-1～1380cm-1The half-value width of the peak in the range is 120cm-1～160cm-1。
7. The negative electrode active material according to any one of claims 1 to 3, wherein the negative electrode active material has a Raman shift of 1300cm-1～1380cm-1The half-value width of the peak in the range is 128cm-1～152cm-1。
8. The anode active material according to any one of claims 1 to 3, wherein the modified polymer coating layer contains a sulfur element and a carbon element.
9. The negative electrode active material of claim 8, wherein the sulfur element accounts for 0.5 to 3% by mass of the negative electrode active material.
10. The negative electrode active material of claim 8, wherein the sulfur element accounts for 0.8 to 1.5% by mass of the negative electrode active material.
11. The negative electrode active material according to claim 8, wherein the carbon element accounts for 0.1 to 4% by mass of the negative electrode active material.
12. The negative electrode active material according to claim 8, wherein the carbon element accounts for 0.5 to 3% by mass of the negative electrode active material.
13. The negative electrode active material according to any one of claims 1 to 3, wherein the negative electrode active material has a peak with a half-value width of 4 ° to 12 ° in a range of 2 θ of 19 ° to 27 ° in an X-ray diffraction spectrum.
14. The negative electrode active material according to any one of claims 1 to 3, wherein the negative electrode active material has a peak with a half-value width of 5 ° to 10 ° in a range of 2 θ of 19 ° to 27 ° in an X-ray diffraction spectrum.
15. The negative electrode active material according to any one of claims 1 to 3, wherein the particle diameter D of the negative electrode active materialv50 is 2-12 μm.
16. The negative electrode active material according to any one of claims 1 to 3, wherein the particle diameter D of the negative electrode active materialv50 is 4-8 μm.
17. The negative electrode active material according to any one of claims 1 to 3, wherein the particle diameter D of the negative electrode active materialv10. Particle diameter Dv50 and particle diameter Dv90 satisfies the following conditions: not more than 0.5 (D)v90-Dv10)/Dv50≤2.5。
18. The negative electrode active material according to any one of claims 1 to 3, wherein the particle diameter D of the negative electrode active materialv10. Particle diameter Dv50 and particle diameter Dv90 satisfies the following conditions: not more than 0.8 (D)v90-Dv10)/Dv50≤2.0。
19. The negative electrode active material according to any one of claims 1 to 3, wherein the specific surface area of the negative electrode active material is 0.5m2/g～5m2/g。
20. The negative electrode active material according to any one of claims 1 to 3, wherein the specific surface area of the negative electrode active material is 0.8m2/g～3m2/g。
21. The negative electrode active material according to any one of claims 1 to 3, wherein the tap density of the negative electrode active material is 0.8g/cm3～1.3g/cm3。
22. The negative electrode active material according to any one of claims 1 to 3, wherein the negative electrode active material has a compacted density of 1.1g/cm measured at a pressure of 5 tons3～1.6g/cm3。
23. The negative electrode active material according to any one of claims 1 to 3, wherein the negative electrode active material has a compacted density of 1.2g/cm measured at a pressure of 5 tons3～1.5g/cm3。
24. A method of preparing the anode active material according to any one of claims 1 to 23, comprising the following steps (1), (2) and (3):
(1) dissolving a certain mass of polymer in a solvent to obtain a solution; wherein the polymer is selected from at least one of polyacrylonitrile, polyaniline, polyethylene, polyacetylene, polyvinyl chloride and polystyrene;
(2) mixing SiOxMixing the particles with the solution obtained in the step (1) to obtain a mixture, wherein x is more than 0 and less than 2;
(3) and (3) mixing the mixture obtained in the step (2) with a certain mass of sulfur powder, and then carrying out heat treatment in an inert atmosphere to obtain the negative electrode active material.
25. The method according to claim 24, wherein before the step (2), further comprising a step (2-1): mixing SiOxThe material is crushed to obtain SiO with certain particle sizexParticles, wherein x is more than 0 and less than 2.
26. The method according to claim 24 or 25, further comprising, between steps (2) and (3), step (3-1): and (3) drying the mixture obtained in the step (2) to obtain a solid, and mixing the solid with the sulfur powder in the step (3).
27. The method according to claim 24 or 25, wherein the mass ratio of the sulfur powder to the polymer is (1-5): 1.
28. The method according to claim 24 or 25, wherein the temperature of the heat treatment in the step (3) is 250 to 450 ℃.
29. The method according to claim 24 or 25, wherein the heat treatment time in the step (3) is 2 to 8 hours.
30. A secondary battery comprising the anode active material according to any one of claims 1 to 23.
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